HYDROGEN UNIT 9

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HYDROGEN UNIT 9

• PREPARED BY PRASHANTH C P
• KV GANESHKHIND PUNE.

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HYDROGEN

• Hydrogen has the simplest atomic structure among
  all the element. However, it exist in diatomic
  (H2) form in nature and is the lightest and most
  abundant chemical element, constituting roughly
  75 of the universes chemical element mass but
  is still the rarest element on the earth about
  0.15 by mass. The name hydrogen is arrived from
  a Greek HYDRO meaning water and GENES meaning
  creator.

By R. Gautham
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DISCOVERY
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POSITION OF HYDROGEN IN THE PERIODIC TABLE
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Isotopes of Hydrogen
Hydrogen has three naturally occurring
isotopes, denoted 1H, 2H and 3H. Other, highly
unstable nuclei (4H to 7H) have been synthesized
in the laboratory but not observed in nature.
Harold C. Urey was awarded Nobel prize to
separate these.
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• Laboratory preparation of Dihydrogen
• It is usually prepared by the reaction of
  granulated zinc with dilute hydrochloric acid.
• Zn 2H Zn2 H2
• It can also be prepared by the reaction of zinc
  with aqueous alkali.
• Zn 2NaOH Na2ZnO2 H2

Sodium zincate
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Commercial Production of Dihydrogen

• Electrolysis of acidified water using platinum
  electrodes gives hydrogen
• 2H2O(l)
  2H2(g)O2(g)
• High purity(gt99.95) dihydrogen is obtained by
  electrolysing warm aqueous barium hydroxide
  solution between nickel electrodes.
• It is obtained as a byproduct in the manufacture
  of sodium hydroxide and chlorine by the
  electrolysis of brine solution.
• 2Na(aq)2Cl-(aq)2H2O(l)
• Cl2(g)H2(g)2Na(aq)2OH-(aq)

Electrolysis
Traces of acid/base
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• Reaction of steam on hydrocarbons or coke at high
  temperature in the presence of catalyst yields
  hydrogen.
• CH4(g)H2O(g) CO(g)3H2(g)
• Water spontaneously dissociates at around 2500C,
  but this occurs at temperatures too high for
  usual process piping and equipment so catalysts
  are required to reduce the dissociation
  temperature. This method is called thermolysis.
• Presently 77 of the industrial dihydrogen is
  produced from petro-chemicals, 18 from coal, 4
  from electrolysis of aqueous solution and 1 from
  other sources

1270K
Ni
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PROPERTIES OF DIHYDROGEN

• Physical properties
• Dihydrogen is a colourless, odourless,
  tasteless, combustible gas. It is lighter than
  air and insoluble in water.

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• Chemical properties
• Reaction with halogen
• H2(g)X2(g) 2HX(g)
  (X F, Cl, Br, I)
• 2. Reaction with dioxygen
• H2(g)O2(g) 2H2O(l)
• 3. Reaction with dinitrogen
• 3H2(g)N2(g) 2NH3(g)
• Reaction with metals
• H2(g)2M(g) 2MH(s) (M is an alkali
  metal)

catalyst or heating
673K,200atm
Fe
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• 5. Reaction with metal ions and metal oxides
• H2(g)Pd2(aq) Pd(s)2H(aq)
• yH2(g)MxOy(s) xM(s)yH2O(l)
• Reactions with organic compounds
• Hydrogenation of vegetable oils using nickel as
  catalyst gives edible fats.
• Hydroformylation of olefins yields aldehydes
  which further undergo reduction to give alcohols.
• H2CORCHCH2 RCH2CH2CHO
• H2RCH2CH2CHO RCH2CH2CH2OH

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USES OF DIHYDROGEN

• The largest single use of dihydrogen is in the
  synthesis of ammonia which is used in the
  manufacture of nitric acid and nitrogenous
  fertilizer.
• Dihydrogen is used in the manufacture of
  polyunsaturated vegetable oils like soyabean,
  cotton seeds etc.
• It is used in the manufacture of bulk organic
  chemicals, particularly methanol.
• CO(g)2H2(g) CH3OH(l)

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• It is widely used for the manufacture of metal
  hydrides.
• It is used for the preparation of hydrogen
  chloride, a highly useful chemical.
• In metallurgical processes, it is used to reduce
  heavy metal oxides to metals.
• It is used as a rocket fuel is space research.

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• Atomic hydrogen and oxy-hydrogen torches find use
  for cutting and weilding purposes. Atomic
  hydrogen atoms are allowed to recombine on the
  surface to be weilded to generate the temperature
  of 400K.
• Dihydrogen is used in fuel cells for generating
  electrical energy. It has many advantages over
  the conventional fossil fuels and electric power.
  It does not produce any pollution and releases
  greater energy per unit mass of fuel in
  comparison to gasoline and other fuels.

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HYDRIDES

• What are hydrides?
• When dihydrogen Combines with other elements to
  form various compounds, that compounds are called
  as hydrides.

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IONIC HYDRIDES

• These hydrides are form from s-block elements.
• Are highly electropositive in character.
• These are crystalline, non-volatile,
  non-conducting in solid state.
• Saline hydrides react violently with water to
  produce dihydrogen gas.
• KH(S) H2O(q) H2 (g) 2electrons.
• Stability of the hydrides decreases down the
  group I and II.
• Lithium hydrides is rather unreactive at moderate
  temperature with Cl2 and O2.SO so it is used to
  synthesize other useful hydride.

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COVALENT HYDRIDES

• - Dihydrogen forms molecular compounds with
  most of the p-block elements, for e.g.
• H2O CH4 NH3.
• Volatile compounds
• These hydrides are further classified according
  to the relative numbers of electrons and
  bonds in their Lewis structure.

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ELECTRON DEFICIENT

• These hydrides have very few electrons for
  writing its conventional Lewis structure.
• Boron family (group 13) forms electron deficient
  compounds.
• These hydrides behave as Lewis acid i.e. electron
  pair acceptor.
• Example Diborane

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ELCTRON PRECISE HYDRIDES

• Carbon family forms such types of hydrides.
• Compound have tetrahedral geometry.
• Example CH4
• These hydrides have the required numbers of
  electrons to write their conventional Lewis
  structure.

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ELCTRON RICH HYDRIDES

• These hydrides have excess number of electrons
  (lone pairs).
• Nitrogen family, oxygen family and fluorine
  family forms these type of hydrides.
• These compounds behaves like Lewis bases.
• Presence of lone pairs of electrons on highly
  electronegative elements like N, O and F results
  in hydrogen bonding.
• Examples NH3 and H2O

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METALLIC HYDRIDES

• These are formed by many d-block elements and
  f-block elements.
• However Mn, Fe and Cobalt family do not form
  hydrides.
• Only 7th group forms these hydrides like CrH.
• These hydrides conduct heat and electricity.
• These are nonstoichiometric and deficient in
  hydrogen.
• Example TiH1.8-2, LaH2.87.

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• Examples
• nickel hydride used in NiMH batteries
• palladium hydride electrodes in cold fusion
  experiments
• lithium aluminium hydride a powerful reducing
  agent used in organic chemistry
• sodium borohydride selective specialty reducing
  agent, hydrogen storage in fuel cells
• sodium hydride a powerful base used in organic
  chemistry
• diborane reducing agent, rocket fuel,
  semiconductor dopant, catalyst, used in organic
  synthesis also borane, pentaborane and
  decaborane
• arsine used for doping semiconductors
• stibine used in semiconductor industry
• phosphine used for fumigation
• silane many industrial uses, e.g. manufacture of
  composite materials and water repellents
• ammonia coolant, fuel, fertilizer, many other
  industrial uses
• hydrogen sulfide component of natural gas,
  important source of sulphur
• Chemically, even water and hydrocarbons could be
  considered hydrides.
• A notable thing is that all solid non-metallic
  metalloid hydrides are highly flammable. But,
  when Hydrogen combines with halogens, it produces
  acids rather than hydrides and they are not
  flammable.

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WATER
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Natural occurrence

• Rain water Purest form of natural water.
• Sea water It is an impure form of water.
• Surface water Include streams, rivers and lakes
  and are most important sources of water for all
  purposes.

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Hydrogen bonding in water
In a hydrogen compound, when hydrogen is bonded
with highly electronegative atom (F,O,N) by a
covalent bond, electron pair is attracted towards
electronegative atom so strongly that a dipole
results i.e., one end carries a positive charge
(H-end) and other end carries a positive charge
(X-end). If a number of such molecules are
brought nearer to each other, the positive end of
one molecule and the negative end of the other
molecule will attract each other and weak
electrostatic force will develop. Thus, these
molecules will associate together to form a
cluster of molecules.
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In water, there is INTERMOLECULAR
H-BONDING This type of hydrogen bonding
increases the boiling point of the compound and
also its solubility in water. Increase in boiling
point is due to association of several molecules
of the compound.
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STRUCTURE OF WATER
s- bond
s- bond
H
H
Two bond pairs and two lone pairs
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Physical properties

• Colourless, tasteless and odourless.
• Freezes at 0o C and boils at 100o C.
• Maximum density is 1.00gcm-3 at 4o C.
• Polar molecule, V-shaped structure.
• Has a high dielectric constant. (78.39)
• Poor conductor of electricity.
• Tendency to associate.
• Universal solvent.
• High values of specific heat, latent heat of
  fusion and latent heat of vapourisation.

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Hydrogen bonding in water and ice.
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CHEMICAL PROPERTIES

• NATURE
• Water is neutral in nature.
• Reaction with metals
• Reacts with active metals and evolves hydrogen.
• It is decomposed by metals like Zn, Mg, Fe, etc.,
  when steam is passed over hot metals.
• Reaction with non metals
• Fluorine decomposes cold water.
• Chlorine decomposes cold water forming HCl and
  HClO.
• When steam is passed over red hot coke , water
  gas is formed.
• Action on nonmetallic oxides
• Acidic oxides combine with water to form acids.
• Action on metallic oxides
• Basic oxides combine with water to form alkalies.

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• Action on hydrides, Carbides, Nitrides,
  Phosphides
• Water decomposes these compounds with liberation
  of hydrogen, acetylene (or methane), ammonia,
  phosphine resp.
• Hydrolysis
• Many salts, specially the salts of strong bases
  with weak acids, weak bases with strong acids and
  weak bases with weak acids undergo hydrolysis in
  water.
• Some salts on hydrolysis form oxy compounds.
• Decomposition
• Water containing either alkali or acid when
  electrolysed gets decomposed into H2 and O2.
• Water of crystallisation
• It combines with many salts during
  crystallisation to form hydrates

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• Water as a catalyst
• Water acts as a catalyst in many reactions.
  Perfectly dry gases generally do not react but
  the presence of moisture brings the chemical
  change. Ammonia and hydrochloric acid gas combine
  only in the presence of moisture.

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HEAVY WATER, D20

• It is used as a moderator in nuclear reactors to
  study the nuclear mechanisms.
• It can be prepared by exhaustive electrolysis of
  water .
• It can also be formed as a by product in some
  fertilizers.

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• It is not radioactive .
• It is used for preparation of other deuterium
  compounds.
• EXAMPLES-
• CaC2 2D20 C2D2 Ca(OD)2
• SO3 D2O D2SO4

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Hydrogen peroxide
Methods of preparation
1. From Barium peroxide
Barium sulphate is filtered off leaving behind
H2O2.
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2. By electrolysis of 50 H2SO4
At cathode
At Anode
H2O2 distills first leaving behind the H2SO4
which is recycled.
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3. By auto oxidation of 2-ethylanthraquinol
The H2O2 obtained by this method is further
concentrated by distillation under reduced
pressure.
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Structure of hydrogen peroxide
Structure and dimensions of the H2O2molecule in
the gas phase
... and in the solid (crystalline) phase.
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Oxidising properties
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Oxidising properties
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Reducing properties
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Reducing properties
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Acidic properties
It reacts with alkalies and decomposes
carbonates.
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USES OF PEROXIDES

• One of the most common uses of hydrogen peroxide
  is as a disinfectant. Spray some hydrogen
  peroxide on surfaces like kitchen counter top and
  wipe with a clean rag. You may even use it to
  disinfect your cutting board.
• Hydrogen peroxide can be used as a mouthwash too.
  You have to dilute the chemical with water and
  use it for rinsing the mouth. This mouthwash is
  also said to whiten teeth. Ensure that you do not
  swallow the liquid, while rinsing.
• Some farmers use hydrogen peroxide as an
  insecticide. They spray diluted form of this
  chemical, on plants, so that the pests and weeds
  get killed, without causing harm to the plants.
• As rocket fuel.
• For bleaching silk, wool, hair and leather

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Do you know?
H2O2 is stored in the bottles lined with wax
because
The rough glass surface causes the decomposition
of hydrogen peroxide.
35 Hydrogen Peroxide is used world wide in
municipal water supplies instead of chlorine to
disinfect and stop the growth of unwanted
organisms. Do you have pure water?
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DID YOU KNOW?
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Handling and storage

• Store in a cool, dry place away from sunlight and
  other sources of heat. 
• Always use non-metallic utensils. 
• Do not allow contact with easily burnable
  materials, such as paper. 
• Always store hydrogen peroxide in the container
  supplied. 
• Replace cap immediately after use - it is
  important that nothing gets in to the
  container as this may lead to the hydrogen
  peroxide breaking down which could result in
  explosions. 
• Store securely.
• Always wear suitable protective gloves. 
• Avoid contact with eyes and face. 
• Do not use on damaged or sensitive skin.
• Wash any residues down the drain with plenty of
  water. 
• Do not burn.

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First aid measures
If hydrogen peroxide gets into the eyes or on the
skin, rinse immediately with plenty of water. If
the symptoms persist, or if it is swallowed, seek
medical attention immediately. Always use water
to dilute and mop up spillages.
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How do we find the normality of given value of
H2O2 ?
10 volume hydrogen peroxide means that 1 ml of
such a solution of hydrogen peroxide on heating
will produce 10 ml of oxygen at N.T.P.
2(2 32) gm 22.4L at N.T.P. 68 gm
or 22400 cm3 at N.T.P.
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Solution
But 10 ml of O2 at N.T.P. are produced from 1 ml
of 10 volume H2O2 solution.
0.03035 gm
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• DIHYDROGEN AS FUEL
• It releases large quantity of heat when
  combusted.
• It can release more energy than petrol.
• Pollutants in dihydrogen when combusted are less
  than pollutants in petrol.

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• LIMITATIONS
• A cylinder of compressed Dihydrogen weighs about
  30 times as much as a tank of petrol containing
  the same amount of energy.
• Dihydrogen gas is converted into liquid state by
  cooling to 20k (requires expensive insulated
  tanks) .

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• Hydrogen economy- an alternative and uses.
• Its basic principle is the transportation and
  storage of energy in the form of liquid
  dihydrogen.
• Dihydrogen is mixed in CNG for use in four
  wheeler vehicles.
• It is also used in fuel cells for generation of
  electric power..

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Thanks